Psoriasis is characterized by massive infiltration of polymorphonuclear leukocytes (PMNL), epidermal hyperplasia and extensive angiogenesis. Eicosanoids such as LTC4, LTB4 are formed in psoriatic skin. High concentrations of 12-R-hydroxy-5,8,10,14-eicosatetraenoic acid (12-R-HETE) are also present. LTB4, 12-R-HETE, 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-oxo-ETE), a newly discovered mediator, are protein chemotactic factors for PMNL. 5-OxoETE is also the most active chemotactic agent for eosinophils which also infiltrating cells in psoriasis. It is not known whether 5-oxo-ETE is formed in skin. 12-R-Hydroxy 5Z,8Z,14Z-eicosatrienoic acid (12-R-HETgammaE), a potent angiogenic factor in the rabbit eye, stimulate endothelial cell proliferation at picomolar concentrations and may be a contributor to the angiogenesis observe in psoriasis. One report describes its formation in rat skin. These mediators possess the biological activity t explain all the pathological symptoms of psoriasis. 5-Oxo-ETB and 12-R-HETgammaE may act on new yet unidentified receptors. LTD is a potent mitogen for human melanocytes, stimulates melanocytes migration an may be involved in the initial steps of melanocyte oncogenesis. LTB4 in the keratinocytes produces LT analogs which might also act on the melanocytes. In spite of recent progress described in this proposal, the mechanism of formation and transformation of these inflammatory mediators in the skin remains largely obscure. The delineation of the inflammatory pathway in psoriasis will provide in the long term a rational approach to drug intervention and therapy. This proposal is aired at the elucidation of the biochemical pathways for the formation and biotransformation of 12-hydroxy- , 12-oxo-eicosanoids, 12-R-HETgammaE, LTB4 LTC4 and 5-oxo-ETE. The objectives of this proposal are two fold. The first is an extensive synthetic program focused on the synthesis of mediators and metabolites, the synthesis of radiolabeled precursors an the synthesis of radiolabeled photoaffinity probes. The second objective is a) the use of synthetic cold an radiolabeled probes for metabolism studies of 12-R-HETE, 12-oxo-ETE, 12- R-HETgammaE, LTB4, 12-oxo-LTh4 and 5-oxo-ETh; b) the use of the photoaffinity probe to characterize the 5-oxo-ETE receptor and the specific 5 hydroxy eicosanoid dehydrogenase; c) the evaluation of the biological and inflammatory properties of the synthetic mediators and analogs in assays such as: chemotaxis in human PMNL and eosinophils, measurement of Ca+ in neutrophils, adherence of neutrophils to endothelial cells, measurement of DNA synthesis and cell proliferation in human keratinocytes and melanocytes. Assays such as guinea pig lung will be used for LTB4 like activity and bronchi strips for LTC4-like contractile activity.